Mechanics: Work and Energy

Work and Energy: Audio Guided Solution

Problem Set WE16, Question 7:

In another episode of Don't Do This At Home, a 79.2-kg man steps off a 1.16-m high bench and lands with his knees and ankles locked. The only cushion for his fall is the 0.585-cm give in the pads of his shoes. Calculate the average force exerted upon his body by the ground as he abruptly stops.
 

 

 

Audio Guided Solution

 

Use the equations below to solve this problem. Cancel terms, substitute and solve.

KE_i + PE_i + W_nc = KE_f + PE_f

0.5•m•v_i² + m•g•h _i + 0.5•k•x_i² + F•d•cos Θ = 0.5•m•v_f² + m•g•h _f + 0.5•k•x_f²

 

Habits of an Effective Problem Solver

• Read the problem carefully and develop a mental picture of the physical situation. If necessary, sketch a simple diagram of the physical situation to help you visualize it.
• Identify the known and unknown quantities in an organized manner. Equate given values to the symbols used to represent the corresponding quantity - e.g., v_o = 0 m/s; a = 4.2 m/s/s; v_f = 22.9 m/s; d = ???.
• Use physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
• Identify the appropriate formula(s) to use.
• Perform substitutions and algebraic manipulations in order to solve for the unknown quantity

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Read About It!

Get more information on the topic of Work, Energy and Power at The Physics Classroom Tutorial.

• Situations Involving External Forces
• Situations Involving Energy Conservation

 

Watch It!

Try our YouTube videos on the topic of ...

• External Energy Transfer
   
• Mechanical Energy Conservation